As a backup protection,distance protection is widely used as line and component protection for each voltage level.In order to ensure the direction,positive sequence voltage is used as the polarization voltage for distance protection.However,the positive sequence polarization voltage may not reflect the pre-fault voltage correetly when the system is in open-phase operating conditions.This paper introduced a mal-operation case of distance protection for a reverse fault,analyzed the disadvantages of using positive sequence polarization voltage,and proposed corresponding solutions.Finally,experiment results of RTDS validate the correctness of the scheme.